To provide mobile communication services to a plurality of users, it is required to physically divide communication path capacity. A multiplexing method and a multiple access method are used to divide the communication path capacity. In the multiplexing method, a transmitter transmits a signal in a frequency division multiplexing (FDM) method or a time division multiplexing (TDM) method when a communication path is used between two base stations. Multiple access methods include a frequency division multiple access (FDMA) method, a time division multiple access (TDMA) method, and a code division multiple access (CDMA) method, in which a plurality of terminals use the divided communication path capacity of one base station.
Among these methods, the frequency division multiple access method is widely used since configurations of antennas, amplification devices, and modulators are simplified, and there is no need to perform complicated synchronization.
FIG. 1 shows a diagram representing a modulation method in a conventional frequency division multiple access mobile communication system.
In the conventional frequency division multiple access mobile communication system, a base station 110 includes a band allocator 112 for each terminal and a modulator 114 following band allocation to each terminal, and a terminal 120 includes a receiver 122 and a demodulator 124.
A transmitter of the base station 110 transmits modulated data to the receiver 122 of each terminal 120 through a radio channel, and the receiver 122 of each terminal 120 restores the data by demodulating the modulated data with the demodulator 124.
However, there is a problem in that performance is reduced since each terminal has different radio channel performance in the above system.
To solve the above problem, an adaptive transmission method for performing channel estimation by the terminal 120 has been suggested.
FIG. 2 shows a diagram representing an adaptive transmission method for performing the channel estimation by the terminal in the frequency division multiple access mobile communication system.
In the adaptive transmission method for performing the channel estimation, a base station 210 additionally includes a pilot signal generator 212, and a terminal 220 additionally includes a channel estimator 222. The pilot signal generator 212 and the channel estimator 222 are not included in the base station of the conventional frequency division multiple access method. The receiver 122 of the terminal 220 is not illustrated in FIG. 2, and will be described assuming that it is included in the demodulator 124.
The transmitter of the base station 210 transmits a pilot signal or a preamble to the receiver of each terminal 220 through the radio channel, the receiver of each terminal 220 uses the pilot signal or the preamble to demodulate data with the demodulator 124, and the channel estimator 222 for estimating a channel frequency response estimates the channel frequency response on each band. Subsequently, channel information on every band is fed back to the base station 210. Then, the band allocator 112 for determining a band allocation method for each terminal determines a band to be allocated to the terminal 220 based on the received channel information. When the band to be allocated to each terminal is determined, the modulator 114 of each band allocated to each terminal modulates data, and adaptively transmits traffic data. Accordingly, performance and capacity in the mobile communication system are increased, which has been suggested in a paper entitled “Computationally Efficient Bandwidth Allocation and Power Control for OFDMA” in IEEE Transaction Wireless Communication Vol. 2 (published 11 2003).
However, in the above method, since channel information on bands which are not allocated to the terminal is also required to be fed back to the base station, overhead of the feedback information is greatly increased, and the receiver of the terminal is required to transmit a large amount of information to the base station. Therefore, the system is deteriorated since power consumption is increased and interference is generated between the terminals. To solve the above problem, a method for transmitting channel information on the bands allocated to the terminal rather than transmitting the channel information on all the bands, and reducing the overhead at the base station without performance degradation, has been suggested in a transaction entitled “Opportunistic Scheduling with Partial Channel Information in OFDM/FDD Systems” in IEEE Vehicular Technology Conference Vol. 1 (published September 2004). However, in the above method, there is a problem in that a desired bit error rate may not be obtained since an average value of channel frequency response values of all the bands is used to perform the modulation for the bands which are not allocated to the terminal.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.